An application running on-premises and on EC2 accesses an S3 bucket over the public internet. EC2 instances connect to on-prem via a Site-to-Site VPN. New regulations mandate that traffic between the application servers and S3 must remain private and avoid public IP addresses. Which solution meets the requirement most cost-effectively?

The correct solution combines an S3 interface endpoint for on-premises access and an S3 gateway endpoint for EC2 instances. An S3 interface endpoint provides private connectivity to S3 from on-premises networks via AWS Direct Connect or Site-to-Site VPN, using private IP addresses. An S3 gateway endpoint allows EC2 instances within a VPC to access S3 privately without traversing the public internet, and it is free of charge. This approach is cost-effective because the gateway endpoint incurs no additional cost, and the interface endpoint is necessary for private on-premises access. Incorrect options: Creating only an S3 gateway endpoint would not provide private access for on-premises servers. Creating only an S3 interface endpoint for both would work but is less cost-effective for EC2 instances, as interface endpoints incur charges per GB processed and per hour, while gateway endpoints are free. The proxy fleet solution is overly complex and expensive compared to using native S3 endpoints.